Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptor superfamily of ligand-activated transcription factors. Three subtypes of PPARs have been cloned from the mouse and human: i.e., PPAR.alpha., PPAR.gamma. and PPAR.delta.. The PPARs are believed to play a role in the regulation of lipid metabolism. They can be activated by fatty acids and have been shown to regulate the expression levels of binding proteins and enzymes involved in fatty acid oxidation.
It has previously been discovered that a certain class of thiazolidinediones are selective PPAR.gamma. agonists. (see, Willson et. al., J. Med. Chem (1996) 39:665-668). Thiazolidinediones are a class of oral insulin-sensitizing agents that improve glucose utilization without stimulating insulin release. For instance, U.S. Pat. No. 4,287,200 discloses certain thiazolidine derivatives having the ability to lower blood glucose sugar levels. In addition, U.S. Pat. No. 4,572,912 discloses thiazolidinedione derivatives having the ability to lower blood lipid and blood sugar levels. These compounds were shown to have the ability to decrease the levels of blood lipid peroxides, blood triglycerides and blood cholesterol.
Moreover, U.S. Pat. No. 5,338,855 discloses thiazolidine derivatives containing a quinone moiety. These compounds were shown to have the ability to reduce insulin resistance in the peripheral tissues and possess the ability to suppress hepatic gluconeogenisis in the liver.
In addition to being anti-diabetic agents which can lower the concentration of glucose and lipids in the blood, U.S. Pat. No. 5,594,015 discloses thiazolidine derivatives as being effective in the treatment of hyperproliferation of epithelial cell conditions, such as psoriasis.
The anti-diabetic effect of the thiazolidinediones and their PPAR.gamma. agonist activity has implicated PPAR.gamma. as the molecular target for the anti-diabetic effects of thiazolidinediones. PPAR.gamma. is predominately expressed in adipose tissue and has been implicated as a master regulator of adipocyte differentiation in pre-adipose cell lines.
In view of the role PPAR.gamma. plays in regulation of lipid metabolism and the antagonistic behavior of thiazolidinediones, there remains a need in the art for new thiazolidinedione derivatives and more effective therapies for diabetes and other ailments. As such, the present invention fulfills these and other needs.